The use of visual display systems in simulators for training purposes, particularly in ground based aircraft trainers, has already shown a constant, steady increase. Today's rapidly increasing technology, along with the increasing cost of operating aircraft, taken together provides the need and creates a demand for simulators for such training purposes.
A primary area of concern in this demand for simulators is that dealing with visual display systems. It is a constant objective in the simulator manufacturing field to provide as much realism for a trainee in the simulator as he would expect to encounter in an actual aircraft. This is particularly true in simulators of military vehicles where the trainee must locate visually targets over a wide field of view. It is desirable also to have an infinity image display to make the scene viewed even more realistic.
Vehicle simulators are used to simulate the actual motion of a vehicle in order that one or more trainees may obtain experience without the use of an actual vehicle. The present invention is applicable to aircraft flight simulators and also is applicable equally to simulators for other vehicles and to apparatus generally for simulating a real life situation.
It was a significant improvement in flight simulation and similar display system when collimation of the displayed image was achieved, that is, by making all image points appear to be at infinity. The problem of providing collimation is complicated because it introduces certain distortions. Optical systems are known which will provide collimated light for a single trainee, but to compensate for the distortions and to provide maximum illumination is still a troublesome problem.
In such known optical systems, distortion may be minimized and illumination may be improved, but in such systems, these two defects have not been able to be corrected or compensated for at the same time without the use of additional components. In U.S. Pat No. 3,784,742 to Burnham et al, several different arrangements are reviewed for correcting distortion and for improving illumination, none of which do it at the same time or do it the same way.
None of the efforts in the prior art to solve the problem of compensating for (or correcting) distortions or to improve the brightness of the projected image, even recognize that these can be accomplished at the same time without the use of additional components. Additional components to do these separately add materially to the overall cost of the system. With a system constructed in accordance with the present invention, a better light transmission is achieved because there are fewer components in which light can be lost.